Isolation and chemical studies were carried out on an antibiotic which was produced by a new streptomyces, Streptomyces humidus nov. sp. From the physical, chemical, and microbiological properties of this antibiotic in crude state, it was found that this antibiotic belonged to the so-called streptomycin-group antibiotics, but differed from streptomycin, mannosidostreptomycin, and hydroxystreptomycin, which are produced directly by streptomycetes. This antibiotic was finally isolated as a pure crystalline sulfate. The physicochemical and microbiological properties of this sulfate and physicochemical properties of its degradation products showed that this sulfate was nothing but dihydrostreptomycin sulfate.